The largest concentration of Democrats in swing-state Ohio will cast presidential primary ballots Tuesday in a county fraught with election problems, on a voting system just 74 days old.

Election watchdogs are worried that votes in Cuyahoga County, with more than 250,000 Democrats among its 1 million registered voters, will be lost because of a hurried switch from electronic touch-screen voting to paper ballots and a new vote counting system.

Sen. Hillary Rodham Clinton's campaign could be at stake. She has lost a string of 11 presidential contests, and a poll this week showed her Ohio lead over Sen. Barack Obama narrowing. Even Bill Clinton says Ohio and Texas, which votes the same day, are crucial to her hopes for a nomination.

Yet it might take well into Wednesday to get results in Cuyahoga County, which is making its second change since ditching punch-card ballots in 2005, a year after President Bush won reelection by winning Ohio.

Merle King, executive director of the Center for Election Systems at Kennesaw State University in Georgia, said it was not the best time to introduce a new system.

"Ohio is again going to be in the public's attention, particularly Cuyahoga County because of its size," King said. "There's never a great time. What you would hope for is a low-profile election."

Many poll workers were unprepared for electronic voting in the 2006 primary, and results were delayed five days because absentee ballots had to be hand counted. In November, vote totals were delayed until almost noon the day after the election because of computer server problems.

Secretary of State Jennifer Brunner pushed the Cuyahoga County Board of Elections to scrap the $21-million system. The idea was to use Ohio's primary, which usually doesn't figure into the presidential nominations, to work out the kinks of the new optical-scan paper ballot system. That would get the county ready for the November presidential election.

But to everyone's surprise, neither Clinton nor Obama has pulled into the clear, so the attention arrived early in Cleveland.

"We were hoping not to have a lot of scrutiny, but we're going to be ready for it," said Inajo Davis Chappell, an elections board member.

Brunner wants 53 other Ohio counties that use electronic voting machines to switch to paper as well, but for the primary she's only requiring them to make paper ballots available to voters who ask for them.

Cuyahoga is counting its votes in one location -- a downtown warehouse -- instead of at precincts, preventing voters from being alerted if their ballots are improperly filled out, so-called second-chance voting.

The American Civil Liberties Union -- which unsuccessfully sued to stop the county from using the system -- and election watchers like Candice Hoke, director of Cleveland State University's Center for Election Integrity, fear that votes will be lost as a result.

The board plans to begin counting in the precincts at the November election but said there wasn't enough time to put that system in place for the primary.

The county expects a voter turnout of more than 30%, comparable to the 34% turnout in the 2004 presidential primary.

"We've asked almost the impossible of this board of elections," Hoke said. "I believe they have a high commitment to an accurate, fair election, but trying to make this kind of transition in 60 days is difficult."